CUSHIONING : U4 cushioning is definitely softer than U2. Probably can be attributed to Lighstrike, but I think it's primarily due to the sockliner... upgraded with an Ortholite-type insert. So underfoot feels more plush - can't quantify if I feel slower/faster.
BOOTIE FIT : Feels like the same last/fit of the U2. Less comfort and fit from the U4 bootie, as the U4 bootie is thinner than the U2. Also, entry into the shoe is more difficult and opening has less stretch than U2.
COMFORT : I've got the same discomfort from the flex pressure on top of the foot. I attribute it to the shape of the toe guard which forces it to flex right in that area. Additionally, there is a pressure point from the edge of the internal reinforcement on the lateral side of the foot (base of 5th metatarsal/pinky toe). I think the pressure on top will improve as material breaks in, but I'm not too hopeful on the lateral side pain.
DURABILITY : Outsole durability visually looks to be the same as U2. They both share tighter herringbone on medial toe side to beef up the wear zones. Toe piece durability doesn't look at durable. 2 hours on the court and I'm feeling they won't last as long.
STABILITY : Feel pretty confident in all movements on court, no concerns from me, and comparable to U2. I appreciate how Adidas focuses on ensuring shoe bends where the foot is supposed to bend - under ball of foot and not the arch. My experience with latest Nike shoes has been a lot of mid foot bending, and that has resulted in a lot of foot fatigue and pain for me. The upper with the reinforcement underneath results in a more firm/stable shoe, but sacrifices in comfort.
In one sentence : Suitable for high level players, the UB4 is a great lightweight shoe that prioritizes a more stable upper over comfort.